A survey of all patents relating to twist drill sharpening apparatus, that were selected during applicant's preliminary novelty search at the U.S. Patent Office will reveal a number of devices designed to serve several purposes. Some of these devices are attempts to develop a portable, convenient, and relatively inexpensive sharpening device, but it appears that they have not accomplished that purpose to the satisfaction of the user, for such devices do not appear to be on the market now. Even in the most recent patent found, U.S. Pat. No. 3,698,140, issued Oct. 17, 1972, the device requires a portable electric drill and is not too convenient to hold. The twist drill is held in a chuck holder, with separate holders for different size drills. The alignment of the twist drill cutting edges in relation to the circular sharpening wheel is not very precise. In fact, the description does not go into much detail on that aspect.
Prior attempts to build a suitable device have gone back to at least 1883. The twist drill sharpening apparatus shown in U.S. Pat. No. 288,069 used a motor driven set of emery wheels arranged with inclined sharpening faces. A twist drill was held in a holder and extended therefrom to have both cutting edges sharpened at once. This arrangment required machinery that many craftsmen do not have. It would not be convenient even for the professional craftsman who wants to sharpen his drills while on a job away from his shop.
In 1886 another device described in U.S. Pat. No. 352,789 used a grinding wheel or grinder and a sliding guide or tablerest positioned above the wheel and guide blocks to hold the implement to be sharpened. Each of the guide blocks appear to have a guide piece that mates with the platform to hold the block and guide its movement. The guide block is described as being slidable along the platform and the tool sharpened by pressing it against the grinding wheel. In this embodiment the twist drill is not guided except by hand pressure and the alignment with the twist drill cutting edge and the grinding wheel is uncertain. Further, the alignment of the twist drill in the guide block does not appear to be described in detail. All these factors determine the quality of the sharpening and it is apparent that there is room for improvement. One of the embodiments (FIG. 5 and related Figures) is designed to hold a twist drill. An index plate is used together with guides to adjust the twist drill by a very complex series of steps. It is apparent that this device is very complicated to build and use.
In U.S. Pat. No. 1,576,313 issued in 1926 an assembly of a motor driven grinding wheel and tool holder is used to sharpen a twist drill. The drill is held in a carrier, apparently by hand pressure and a block is adjustably arranged to position the twist drill end. A straight edge part of the carrier is used to aim the twist drill cutting edge. A pedestal supports the twist drill carrier at an angle to the grinding wheel, corresponding to the angle between the cutting edges and the axis of the drill. An embodiment shown in FIGS. 4 through 6 involves a separate apparatus to position the twist drill in the carrier before it is placed on the sharpening pedestal. A magnifying glass is used to focus on the straight edge and aim the twist drill cutting edge. It is apparent that this sharpening device requires precise mechanical fittings and adjustments. Also, the twist drill must be moved to separate pedestals. Also, the twist drill carrier must be moved to a new position for the other cutting edge to be sharpened. It would be desirable if some of these requirements could be avoided or minimized, to have a more simplified twist drill sharpening device that can be hand held, is portable, and is relatively easy to operate.
Some of the hand-held twist drill sharpening devices have required re-positioning the twist drill to sharpen both cutting edges, as in U.S. Pat. No. 2,408,544, or use of a carrier that is hand manipulated against a grinding wheel, as described in U.S. Pat. No. 2,821,820. One of the features that is not provided is a simplified and reliable way to align and hold the twist drill relative to sharpening surfaces that can guide the sharpening tool.
Articles have described the use of optical devices, like a hand magnifier with indices to measure drill wear and the cutting edge angle. These articles found in the search are "Design News", page 12, Apr. 28, 1958, Volume 13, No. 9, and a brochure dated in 1959 by Steptool Corporation, 3613 East Olympic Boulevard, Los Angeles, Calif. Each of these articles were found in the Patent Office search files, in the Examiners' offices in Class 51, Sub-class 219.